I used G27 pedals with the Nixim brake mod for a number of years and although
they work well I wanted some top mounted GT style pedals to hopefully get a better feeling
of immersion so I decided to make my own.

For the main structure, I used 50mm x 50mm and 30mm x 15mm aluminium box section and
10mm stainless steel rod to hold it all together. I produced a basic CAD design and g-code
files for CNC which are available
here although they could just
as easily have been cut and drilled by hand.

For the electronics, I used the Leo Bodnar
BU0836-LC Load Cell Joystick Controller which has a single load cell interface and multiple
inputs for analogue devices (eg. potentiometers and hall sensors) and digital inputs for
buttons and switches.

The load cell I used for the brake is a 0-30kg model bought from China which results in a
fairly light pedal so I may swap that for a higher rated model in the future. The model
I have is a Shenlen SL602 which is wired as WHITE = +5V, RED = -IN, YELLOW = +IN and BLACK = GND.

For the clutch and accelerator I initially used A1302 Hall Sensors which are contactless and in
theory should maintain a smooth operation over the long-term.

Update: For unknown reasons I had trouble getting the hall sensor on the accelerator
to stay properly calibrated between sessions so I decided to replace it with a potentiometer
(ALPS 10k RK09711110K) and a traditional linkage which is working great so far.

Choosing springs was mostly trial and error. I ended up with the brake spring being
27mm (OD) x 83mm x 5mm and the clutch as 17.5mm (OD) x 90mm x 2.8mm. I am still testing some
different accelerator springs. The one I am currently using is approximately 12.5mm (OD) x 80mm x 1mm.
My advice is just to buy a few springs so you can test how the pedals feel with different strengths.

The pedals are fully adjustable for separation, reach and stroke but as I always left-foot
brake in games I spaced them fairly equally although it would be straightforward to set them
for heel-and-toe operation.

I don't think these pedals will make me any quicker but they do feel a lot more like
driving a real car than my G27's so are good for improving immersion.